1. Field of the Invention
The invention relates to loudspeaker (hereinafter “speaker”) enclosures. More particularly, the invention relates to a ported speaker enclosure and a method of extending low frequency response of a speaker.
2. Description of the Related Art
A speaker enclosure greatly enhances the acoustic fidelity of sound produced by a speaker above that produced by a bare speaker driver without a speaker enclosure.
In the nineteenth century, Hermann von Helmholtz, a German physician and acoustic engineering pioneer, discovered a type of acoustic resonator known as the Helmholtz resonator. The Helmholtz resonator is a type of acoustic resonator consisting of a closed volume of air connected to the atmosphere by a short channel or pipe. The natural springiness of the enclosed air reacts with the mass of air in the pipe, which results in a tuned resonating tone that is called the fundamental tone for the pipe.
In the 1930's Jensen Company began to market a product called the “bass reflex speaker”. The bass reflex speaker is a speaker enclosure that contains an opening below the speaker driver. The design of the bass reflex opening is more commonly called today as a “vent” opening port.
Two of the audio field's most respected scientists, A. N. Thiele and Richard Small, devoted much research to the analysis of the bass reflex speaker. Thiele and Small discovered that a vented enclosure acts as a resonant box even without the speaker driver mounted into the box. Thiele and Small concluded that the addition of an opening into a box created a resonator similar in theory to the Helmholtz resonator. The research of Thiele and Small also led to the creation of audio industry standards for testing acoustic drivers and speaker enclosures. Specifications commonly referred to as the Thiele or Small parameters are often used to characterize a speaker driver and a speaker system.
By the 1950's, the bass reflex speaker had been modified and a popular method implemented into speaker enclosure designs was the implementation of a duct or port, which is typically an internal tube mounted onto the opening below a speaker driver. The purpose of the duct or tube was to eliminate the resonating frequencies being produced inside the speaker enclosure and channel this information outward towards the listener. Acoustic engineers found that the implementation of the internal duct or tube created a more “boomy” response beyond that of the vent method used by the bass reflex speaker.
The numerous variations of musical styles rely on a fairly consistent choice of instruments. The instruments can include, for example, stringed, wind, and percussion instruments. Percussion instruments, such as the kick drum, create low frequency information. Cymbals and the hi-hat create high frequency information. Such percussion instruments have become standard instrumentation heard and used in contemporary music.
Improvements to the audio fidelity produced by speaker drivers and through speaker enclosures have been sought. It may be advantageous for an audio speaker product to be designed to deliver a full range of audio response. Such a full range speaker system should produce an audible response that includes low, mid and high frequency information.
Additionally, speaker enclosure systems are not limited to theater and audio reproduction environments. Over the course of 50 years, society has seen rapid growths in computers and electronics. Theater, audio, and computer markets share a common objective of creating innovative solutions to improve the quality of reproduced sound and thus keep consumers buying products. Successful companies continually strive to produce high tech innovative designs at a competitive price. For audio engineers, this typically means designing an improved audio solution at a lower cost.
The need to produce cost effective solutions leads to reduced numbers of electronic components. Cost constraints further compound the difficulties audio engineers face when designing an acceptable high fidelity and full range audio solution.
These challenges have acoustic audio engineers reviewing acoustic history in search of methods to create variations of founded theories and to implement these variations into successful audio designs.